1. Field of the Invention
The present invention relates to a Braun tube, and more particularly, to a frame for supporting a shadow mask fitted to a panel of a Braun tube.
2. Background of the Related Art
The Braun tube in a TV receiver having red, green and blue fluorescent materials become luminous by a video signal for reproducing a color image. FIG. 1 illustrates a related art color Braun tube.
That is, the related art Braun tube is provided with a panel 1, a funnel 2 and a neck portion 12. There are stud pins 3 and a fluorescent surface 4 having a fluorescent material layer formed thereon on an inside surface of the panel 1, and there is a shadow mask assembly in the panel 1. The shadow mask assembly has a frame 8, a shadow mask 9 supported by the frame inside of the frame 8, and a spring 10 fastened between the frame 8 and the stud pin 3 for supporting the frame 8 from an inside of the panel 1. There is a bead 8a formed on an inside surface of the frame for supporting a skirt portion 9b of the shadow mask 9, and a flat portion 8b at each corner of the frame for smoother coupling with the spring 10. And, there is an inner shield 11 in rear of the frame for preventing deviation of a path of electron beams 5 caused by an external geomagnetism or leakage magnetism.
The shadow mask assembly should meet the following characteristics for smooth operation of the Braun tube.
First, the thermal expansion of the shadow mask components caused by the electron beams 5 during operation of the Braun tube should be suppressed. The thermal expansion of the shadow mask caused by the electron beams 5 hitting the shadow mask causes doming in which a displacement of the shadow mask occurs.
Second, the rectangular frame 8 should be always held fixed at one position inside of the panel 1, because the howling of the shadow mask 9 occurring during operation of the Braun tube, or by external impact, deteriorates color selection performance of the shadow mask 9.
Third, the variation of landing caused by geomagnetism with an operation direction of the Braun tube should be small, because, though the electron beams 5 should pass through respective slits 9a in the shadow mask 9 in a state wherein initially set emission angles are maintained exactly, the external magnetism affects paths of the electron beams, causing the electron beams 5 to deviate from their exact positions.
In the related art, in order to meet the requirements for the Braun tube, materials of the shadow mask 9 and the frame 8, shape and material of the spring 10, material and shape of the inner shield 11 are modified, appropriately, particularly the shadow mask is formed of an invar alloy for suppressing the doming caused by the thermal expansion to the maximum, because the invar alloy is an approx. 36% Nixe2x80x94Fe alloy with a very low thermal expansion coefficient. However, even though deformation of the shadow mask 9 by the heat is very small, deformation of the frame 8 is very severe considering that in general the frame 8 has a thermal expansion coefficient of 1.2xc3x9710xe2x88x925. Accordingly, in the related art, a structure (or shape) of the spring 10 which supports the frame 8 inside of the panel 1 is varied for reducing the misalignment. However, since the spring should be fabricated considering, not only the supporting of the frame 8, but also the misalignment of the shadow mask 9, the design of the spring has been difficult. And, in the related art, the external magnetism is shielded by providing the inner shield 8 fitted from rear side of the frame 8 along an inside of the panel 1 for adjusting a magnetic flux density at a center in the inner shield and magnetic flux density outside of the inner shield, appropriately. However, the related art frame 8 has a size generally smaller than the panel 1. Accordingly, the space in which the electron beams 5 pass through on the inside space of the frame is small such that a magnetic flux density at the center portion of the frame 8 becomes similar to the magnetic flux density at a periphery of the inside of the frame. That deteriorates the magnetic shielding effect sharply, and the low height of the frame 8 causes the magnetic flux to fail to concentrate into long and short sides, and corners of the inner shield 11, resulting in the magnetic flux density at the center and the periphery of the inside of the panel to be similar. The similar magnetic flux densities can not reduce the path variation caused by the external magnetism, deteriorating the external magnetism shielding effect sharply, which increases variation of landing of the electron beams.
Taking the aforementioned different problems and the current trend in which the Braun tube is gradually planarized into consideration, there is a limitation in that the aforementioned various requirements for the Braun tube are met by varying materials, or shapes of the shadow mask 9, the spring 10 and the inner shield 11. That is, the small enclosing volume of the related art frame 8 leads to a greater temperature rise of the frame 8 by the electron beams 5, and the low height of the related art frame 8 leads to a greater distortion of the shadow mask in fabrication or in operation of the Braun tube because the related art frame 8 can not enclose an outer circumference of the shadow mask 9 formed in correspondence to the planarization of the panel 1, adequately. The low shielding effect in a space between the panel 1 and the shadow mask 9 caused by the low height of the frame 8 results in a large variation of the landing. In view of the foregoing discussion, it can be known that, since an inside surface curvature of a panel becomes greater than the curvature of the related art panel 1 as the Braun tube becomes the flatter, the height of the frame 8 should be made higher for minimizing variation caused by the geomagnetism in change of direction. However, mere increase of an overall frame height along with the increase of the inside surface curvature of the panel 8 may in turn cause a problem in that doming and howling can not be prevented, effectively.
Accordingly, the present invention is directed to a frame in a Braun tube that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide a Braun tube which is stable from influences of doming, howling and geomagnetism.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, the Braun tube includes a shadow mask, a panel for supporting the shadow mask, stud pins fitted between the shadow mask and the panel, and a frame of substantially rectangular form having a long side with a height in a range of (0.8-0.9)xc3x97(a height from a center of the stud pin to a central point of an inside surface of the panel), and a short side and a corner side each with a height in a range of (0.7-0.85)xc3x97(the height of the long side).
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.